1. Technical Field
The present invention relates to valve seat inserts for internal combustion engines and methods of making the same, and more specifically, to valve seat inserts that are precision formed and surface treated prior to insertion into internal combustion engines.
2. Related Prior Art
Valve seat inserts produced by known monolithic or composite methods may suffer wear in certain engine applications or they may cause wear of other engine parts such as the mating valve. In using monolithic or composite valve seat inserts, it is necessary to finish machine the seating surface after insertion into the cylinder head or engine block. In order to do this finish machining, the material employed in the insert must have some amount of machinability, which, in turn, may compromise the material""s wear resistance.
When using monolithic material, it is normal practice to produce valve seat inserts out of the monolithic material via casting, wrought, or powder metallurgy practices. The valve seat inserts are then inserted into the cylinder head or engine block, and the seating surface is machined. The wear resistance of the insert""s seating surface is thus the same as the bulk monolith from which the insert has been made, and is generally susceptible to wear problems.
Composite type inserts have also been used, with either a weld overlay or a bimetallic power metallurgy product, with a wear resistant material applied over a lower alloy substrate. However, the valve seat is first inserted into the cylinder head or engine block, and the seating surface is then finish machined after insertion. This finish machining after the wear resistant material has been applied compromises the resistant material, and makes the valve seat insert more susceptible to wear.
The present invention is a substantial modification over existing processes used to produce valve seat inserts. The invention overcomes the above limitations of the prior art by precision forming the valve seat insert and then performing a wear resistant or surface hardening treatment upon the valve seat insert prior to inserting the insert into the engine block. The invention also allows for the use of coating/surface treatments having very thin layers that would be completely removed if any machining were subsequently done after treatment. In a preferred embodiment, the coating/surface treatment typically produces less than 0.05 mm dimensional change on the surface of the insert.
Specifically, the valve seat insert is formed, and the seating surface of the valve seat insert is precision machined. The precision formed seating surface of the valve seat insert is then hardened using a hardening technique. In some embodiments, the hardening step occurs by applying a wear resistant coating or surface treatment to the precision seating surface. The coating or treatment chosen is such that minimal dimensional changes are produced in the precision seating surface. Finally, the precision formed and hardened valve seat insert is inserted into the cylinder head or block of the engine without the need for additional machining.
Before embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of the articles, composition or concentration of components, or to the steps or acts set forth in the following description. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.